The radiation characteristics of an antenna may be determined by measuring the antenna field on an imaginary surface crossed by the radiated power. This measurement surface typically is planar, cylindrical or spherical. Said measures naturally will usually be performed on the user's site.
The measuring device generally is called a measure probe. The appended FIG. 1A schematically illustrates an example of a prior art measure probe.
Such a measure probe 1a essentially includes the following components: a radiating element 13 carried con a support 12 and a probe mount 10. This mount 10 also can act as a support for various electronic circuits for converting and processing the signals received by the probe 1a. The support 12 and the radiating element 13 constitute the probe proper.
The radiating element 13 can have several shapes, depending upon the precise application concerned, the frequency range to be measured, the polarization of the waves emitted by the antenna being tested, etc. Significant examples of the radiating element 13 may be of the slit or dipole type. It should be clearly understood that the word “radiating” indifferently applies to the emission or reception of waves. Finally, the support 2 of the radiating element 13 may be fastened on the mount 10 in an irremovable or a removable manner. The fastening member usually comprises a plate associated with an absorbing element 11a, which will strongly attenuate the received radiation within the range of the frequencies to be measured.
In a well-known manner, determining characteristics of an antenna being tested, such as its radiation diagram for instance, first requires that the measure probe itself be perfectly characterized. Not only a certain number of measuring parameters, but also the probe behavior when immersed in an electromagnetic field, namely need to be known. Even a small size measure probe will not stay “neutral” with respect to the electromagnetic field to be measured. It will interact with it and potentially disturb it.
Characterizing or, in other words, calibrating a measure probe includes determining its radiation diagram, its polarization properties, its gain, and the input reflection coefficient(s) on the probe port(s).
This procedure usually is performed on a so-called calibration site, different from the site where a potential user will erect the measure probe. It usually is a high precision measurement site, where all measuring parameters can be mastered. All the measure probe characteristics are then perfectly defined by a calibration data set.
The measure probe 1a can then be delivered to a potential user, with its calibration data set, for on site tests of an antenna. If however the performances of the measure probe, after its erection on site, are different from the performance previously determined during calibration, the reliability of the measured data of the antenna being tested is questionable.
The FIG. 1B schematically illustrates the characteristics measurement procedure for an antenna 2 on the testing site. The antenna 2 being tested is fixed and emits a radiation with certain determined characteristics, to be measured. The measure probe 1a, on the other hand, is movable in space, on a predetermined surface (a plane for instance), as previously indicated. For this purpose, the measure probe 1a is mounted on the movable carrying device 3, which is moved along a determined path for scanning the above mentioned surface, advantageously under control of computerized means. The measures performed at each point are recorded and real time processed.
A major drift source between performances respectively obtained on the calibration site and the measurement site may be found in the differences in the erection of the measure probe 1a at both sites. A solution consequently needs to be found, i.e. in practice, arranging an appropriate means that will allow eliminating the harmful influence of the erection of the measure probe 1a. 
Eliminating for its major part the influence of the mounting assembly of the probe 1a is relatively simple on the calibration site (FIG. 1A), just by an appropriate digital processing of the calibration data. As previously indicated, the calibration site characteristics namely are perfectly known, repetitive and mastered. The calibration source characteristics also are well known.
The environmental characteristics however are different for each measurement site (FIG. 1B). The exact characteristics of the radiation source, i.e. the antenna 2 being tested, by definition are unknown since they precisely are the objects of the measurement. Mainly the carrying device supporting the probe is there normally different from its supporting assembly on the calibration site.
Using the calibration data set as it stands consequently is impossible if high precision measurements are required.
Various prior art solutions were proposed as attempts for solving this problem. The FIGS. 2A and 2B illustrate one of those proposed solutions. Elements that are common with those of the previous figures are designated by the same references and will only be described again as needed.
This solution was described in the following documents, which can be advantageously referred to for additional details:                the article “Accurate gain measurement on small aperture antennas”, Franck JENSEN and J. LEMANCZYK, “Proceedings of 14th ESA Workshop on Antenna Measurements”, WWP-028, May 6-8 1991,        and the article “The calibration probes for near-field measurements”, Franck JENSEN and J. LEMANCZYK, “AMTA Symposium”, pp. 9.5-9.10, Oct. 7-11 1991.        
As compared with the measure probe 1a of FIGS. 1A and 1B, the present measure probe, now called 1b shows a different structure, essentially because an absorbing element 11b now is an integral part of the measure probe proper. As FIG. 2A more particularly illustrates, the absorbing element 11b is directly fastened to the support 12, behind the radiating element 13.
As illustrated in FIG. 2B, an additional fixed absorbent element 14, with a slit 140 that allows the measure probe 101b to be moved on the movable carrying device 3, is provided on the measurement site.
This solution however suffers from a certain number of inconveniences. The absorbing elements namely are made of lightweight and brittle materials. Both a good reproducibility and a stable shape, from the point or view of the electrical properties, consequently are difficult to guarantee.
It is the object of the present invention to overcome the deficiencies of the prior art devices, some of which were just described.